1. Field of the Invention
This invention relates generally to the methods and systems for detection of very small amount of trace chemicals by employing light scattering probes. More particularly, this invention relates to an improved light scattering probes and detection system based on a novel process to fabricate a sensing chip with nano-structured noble metal surface with improved configurations to detect the trace chemicals with significantly improved detection sensitivity.
2. Description of the Prior Art
Historically, one of major limitations of Raman spectroscopy application is the weak Raman scattering signals for trace chemical detection. It is known in the art that there is a potential solution by employing roughened or the nano-structured sensing surface to generate scattering signals of higher intensity. Specifically, the nano-structured materials have found numerous applications in sensing, bioscience, materials science, semiconductor, etc. One of the promising applications of sensing technologies with nano-structured materials is Surface Enhanced Raman Spectroscopy (SERS) and Surface Enhanced Resonance Raman Spectroscopy (SERRS). It has been discovered that the Raman scattering, signal can be enhanced by 104˜1014 times when molecules are adsorbed on a nano-structured noble metal (such as Ag and Au, but not limited to Ag and Au) surface compared to normal Raman scattering. Specially, Raman scattering signal gets remarkably enhanced if the surface nanoparticles are isolated. The enhancement is determined by several factors, among them, the dimensions of the nano-particles and the distance among these nanoparticles on the surface are very important. It is found that as the scale of these nanoparticles decreases, the signal enhancement of Raman scattering increases. Further, as the distance between neighboring nanoparticles islands varies, the enhancement effect of Raman scattering also varies. However, the conventional technologies, for example, VLSI lithography technology, are still encountered with technical difficulties to fabricate nano-structure surfaces with reduced dimensions of the nano-particles and reduced distance among these nano-particles on the surface to achieve scattering signal enhancement.
The very limited availability of non-contaminated nano-structured noble metal surface is still a major difficulty faced by those of ordinary skill of the art in applying the technologies of Surface Enhanced Raman Scattering (SERS) and Surface Enhanced Resonant Raman Scattering (SERRS) for trace chemical detection. A non-contaminated nano-structured noble metal surface is required to conveniently deploy in the field for molecular adsorption and subsequent measurement. Due to this limit availability, even though the detection of trace chemicals can be achieved a part-per-billion (ppb) level, the techniques of applying SERS and SERRS for detecting trace of explosives and/or other chemical materials still have very limited applications.
The technologies of applying SERS and SERRS for detecting trace chemicals were described in many published papers such as “Probing Single Molecules And Single Nanoparticles by Surface Enhanced Raman Scattering”, Shuming Nie and Steven R. Emory, Scince, 1997, 275, 1102-1106; “Surface Enhanced Raman Spectroscopy of Individual Rhodamine 6G Molecules on Large Ag Nanocrystals”, Amy M Michaels, M. Nirmal, and L. E. Brus. J. Am. Chem Soc. 1999, 121, 9932-9939; “Single Molecule Detection Using Surface-Enhanced Ramam Scattering (SERS)”, Katrin Kneipp, Yang Wang, Harald Kneipp, Lev L. Perelman, Irving Itzkan, Physical Review Letter, 78, 1997. 1667-1670; “Nanosphere Lithography: A versatile Nanofabrication Tool for Studies of Size-Dependent Nanoparticle Optics”, Christy L. Haynes and Richard P. Van Duyne, J. Phys. Chem. B 2001, 105, 5599-5611.
However, these publications do not provide an effective method to produce and package the non-contaminated nano-structured noble metal surface to achieve field applications of SERS and SERRS for trace chemical detection. Furthermore, none of these publications provide method to fabricate nano-structured materials with well-controlled nano array that have reduced and optimized dimensions of the nano-particles and reduced and optimized distances among these nano-particles on the surface to achieve scattering signal enhancement.
Therefore, a need still exists in the art of design and manufacture of optical probes for trace chemical detection by providing new and improved methods to fabricate nano-structured materials with Raman scattering signal-enhancing surfaces and improved detector configuration for packaging and deploy the optical probes such that the above discussed difficulties and limitations can be resolved.